In a power system such as a power transmission line, a power plant, or a substation, conventionally a surge arrester is provided to remove excess voltage and protect the power system and electrical equipment. Among such surge arresters, a polymer surge arrester has a structure such that a plurality of disc-shaped nonlinear resistors mainly containing zinc oxide are stacked, and an electrode is disposed at each of upper and lower end portions thereof, for example. Further, for increasing rigidity, a plurality of insulating rods for fastening the nonlinear resisters are disposed around the nonlinear resistors, and these insulating rods are fixed with a plurality of metal plates or insulating plates to prevent positional displacement of them.
The above-described components are generally called internal elements. Outside these internal elements, an insulating outer skin is formed by casting an insulating resin. In this casting process of the insulating resin, the insulating resin is injected at a high pressure (about 6 MPa to 10 MPa for example) to expel residual air in the insulating resin and air sucked therein during the casting to the outside of the insulating outer skin, thereby preventing occurrence of defect in appearance.
As described above, when the polymer surge arrester is produced, the insulating resin is injected at a high-pressure (about 6 MPa to 10 MPa for example) in the casting process of the insulating resin. Further, the viscosity of the insulating resin at this time is not so high. The viscosity is about 50 Pascal-seconds (Pa·s) for example. Accordingly, the insulating resin may enter among internal elements. In this case, there may occur a contact failure between conductive faces, decrease in energy absorption capability due to reduction in conductive areas of the nonlinear resistors, and the like.